64 THE VOYAGE OF H.M.S.' CHALLENGER. 



of a colony always agree in sex, so that it appears more probable that the irregularity in 

 size in this case is due to the prevalence of a type of budding similar to that which 

 obtains in Leiopathes. In the Schizopathinse, on the other hand, I have failed to recognise 

 any interposition of smaller zooids between those of normal size. A difference in size is 

 often to be seen, it is true, but this only affects the gonozooids and depends on the 

 condition of the reproductive organs. In other respects the regularity in size is most 

 marked (cf. PI. VIII. fig. 1), and contrasts forcibly with the arrangement in Leiopathes. 

 In this case new zooids appear to be added chiefly, if not entirely, at the apex of each 

 branch, where there is a thickened mass of tissue as yet undifferentiated. 



CCENENCHYMA. 



The ccenenchyma consists of the basal portions of the polyps with their connections 

 with adjoining polyps. Its relative importance varies very much in different genera. 

 In the genus Cirripathes it forms a sheath around the relatively thick sclerenchyma in 

 which the polyps are imbedded. In this genus the interzooidal areas are divided by 

 means of mesogioeal septa into a number of canals having a course mainly transverse to 

 the sclerobasic axis. These communicate with the base of each zooid in the manner 

 shown in PI. X. fig. 13. Whether Stichopathes agrees with Cirripathes in having such 

 a type of interzooidal communication is uncertain. Pourtales recognised certain more 

 transparent areas in the interzooidal tissue of Stichojmthes pourtalesi, but did not make 

 sections. The fact that Stichopatlies, like the branched Antipathidse, has the zooids 

 arranged in a single longitudinal series, would lead one to suppose that it possesses 

 a similar means of intercommunication between the zooids. 



In Leiopathes and other genera with a branched sclerenchyma the zooids are usually 

 distributed in a single row on one aspect of the skeleton only. In these cases the fused 

 bases of the polyps form a hollow tube in which the sclerenchyma is formed. The 

 three layers of the polyps are all represented in the ccenenchyma. Externally there is 

 a layer of ectoderm continuous with that of the body-wall of each polyp, in the middle 

 a layer of mesoglcea, and internally a layer of entoderm. At a point opposite the polyps 

 a slender longitudinal mesogioeal septum occurs passing from the mesoglcea for a 

 short distance towards the zooidal ccelentera. This becomes thickened at the free 

 margin, and contains a large central lumen lined by the axis epithelium. In this cavity 

 the sclerobasic axis is formed, which ultimately fills up the whole lumen. Thus the 

 sclerenchyma is contained within a dilation of a free longitudinal septum inserted into 

 the mesogloea of the ccenenchyma at a point opposite the zooidal surface. The skeletal 

 sheath also includes a layer of entoderm continuous with that of the polyps, which forms 

 the median portion of the floor of their ccelentera. 



